Albert Einstein famously said “Everything should be as simple as possible, but not simpler” in reference to physics and its explanations of the Universe.
It might also apply to PowerPoint presentations, where it is too easy to clutter slide with too many bullets or too much information and detail. For example, a chart with comparisons of twenty products across three sales regions for the last four quarters – with all the individual sales figures attached to each part of the stacked bar, of course.
Don’t do it. Keep it simple. Provide enough information in the visual aid to make the point (eg Widgets are selling more than ever, and sales in Toyland are decreasing) but no more than that.
Use the speaker’s notes to provide you with the extra detail if you need to refer to the numbers, and include these notes in the handout so people can digest them later if they want to. Think about using some hidden slides so you have a selection of related charts and / or figures which you can show in response to a direct question, but will not bore the audience with if they seem uninterested (or simply happy to take your conclusions at face value).
Handouts are also the right place for giving the source of your data and any appropriate caveats such as how many people were surveyed in a poll, or what exchange rate has been used to compare sales across currencies.
A good technique to deliver a more professional presentation is to think about what the audience would write down if there were no handouts. What would be the really important things they chose to take away? So why try and ram anything else through their eyeballs and into their brains?
Footnote: you can make your own images of Einstein’s blackboard musings here: http://www.hetemeel.com/einsteinform.php